This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-030727, filed Feb. 8, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a magnetic recording/reading apparatus of a perpendicular magnetic recording system and a magnetic recording medium used therein.
For the requirement of improving recording density in the magnetic recording it has been clarified that it is difficult to manage the reduction of the medium noise and the improvement in the resistance to the thermal decay.
One of the methods for solving the problem is to use a material that permits increasing the magnetic anisotropy energy owned by the layer of a magnetic recording medium. However, in the case of using a material having a large magnetic anisotropy field in an attempt to increase the anisotropy energy, a problem is generated that it is difficult to record information sufficiently with a writing head in a magnetic recording medium obtained by using the particular material. On the other hand, in the case of using a material having a large saturation magnetization without increasing the intensity of the anisotropy field, the magnetostatic coupling among the drains is increased so as to make it difficult to suppress the noise.
Also studied in this technical field is a perpendicular magnetic recording system in which the recording is performed by achieving the magnetization in a direction perpendicular to the planer direction of the magnetic layer. In this system, a demagnetizing field by the adjacent bit does not exert on the magnetization transition region unlike the longitudinal recording in which the magnetization takes place in the longitudinal direction. In this system, a magnetization from the adjacent bit exerts in a direction of stabilizing the magnetization in the magnetization transition region and, thus, this system is stable in a recorded state at a high density and is considered advantageous for the high density recording. Since the perpendicular recording is capable of maintaining a high resolution even if the magnetic film has a large thickness, compared with the longitudinal recording medium, the perpendicular recording is considered advantageous in the thermal stability, too. Such being the situation, the perpendicular recording has come to attract attentions in this respect, too. However, in the case of the perpendicular magnetic recording system, it is reported that the influence of the demagnetizing field within its bit is strongly received because of the thin film shape effect the low recording density, with the result that the reduction of the reproduction output is large in the low recording density. It follows that it is now necessary to improve the resistance to the thermal decay in respect of the perpendicular recording system, too.
It is pointed out that a double-layered recording medium consisting of a magnetic recording layer and a relatively thick soft magnetic layer formed below the magnetic recording layer, which is also being studied in the respect of thermal stability nowadays, is not a perfect solution. In the perpendicular magnetic recording medium, it is effective to increase the anisotropy energy of the magnetic layer as in the longitudinal recording medium. However, if the anisotropy is unduly increased, it is difficult to perform information writing with a head. Therefore, it is necessary to take measures for the resistance to the thermal decay without increasing anisotropy energy.
A first object of the present invention, which has been achieved in an attempt to solve the above-noted problems inherent in the prior art, is to provide a magnetic recording medium used in a perpendicular recording system, which permits improving the resistance to the thermal decay, the recording resolution, and the medium S/N without increasing the head magnetic field.
A second object of the present invention is to provide a magnetic recording/reading apparatus, which permits improving the resistance to the thermal decay and also permits performing a magnetic recording of a high recording resolution and a high medium S/N without increasing the head magnetic field.
According to a first aspect of the present invention, there is provided a magnetic recording medium comprising a substrate; and
a perpendicular magnetic layer formed on said substrate and having an anisotropic magnetic field Hk and a saturation magnetization Ms which satisfy the following relation:
2 less than Hk/4xcfx80Ms less than 5.
According to a second aspect of the present invention, there is provided a magnetic recording/reading apparatus, comprising:
a magnetic recording medium;
a drive mechanism configured to support and rotate said magnetic recording medium; and
a magnetic head configured to record/reproduce information in and from the magnetic recording medium;
wherein said magnetic recording medium has an anisotropic magnetic field Hk and a saturation magnetization Ms which satisfy the following relation:
2 less than Hk/4xcfx80Ms less than 5.
According to the present invention, the value of Hk/4xcfx80Ms is defined to fall within a range of more than 2 and less than 5 so as to make uniform the resistance to the thermal decay of magnetic particles in the magnetic film. As a result, it is possible to make uniform the magnetic reversal field of magnetic particles of the magnetic recording medium so as to carry out the magnetic recording of a high recording resolution and a high medium S/N.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.